This invention relates to an organophilic clay having functions of being dispersed in a high polar organic solvent and gelling the solvent, a method for preparing the same and a gelling rheological control agent.
Clay minerals are divided into a layer silicate mineral and an amorphous mineral, and the majority of which is occupied by the former. The layer silicate mineral has sheets in which SiO.sub.4 tetrahedral sheets are arranged to a two-dimensional network structure. Among them, a 2:1 type layer silicate mineral has a laminated structure of several to several tens of silicate sheets having a three layered structure in which a magnesium octahedral sheet or an aluminum octahedral sheet is sandwiched between two sheets of silica tetrahedral sheets.
A sheet of an expandable layer silicate has a negative electric charge, and the electric charge is neutralized by the existence of alkali metal cations and/or alkaline earth metal cations in the interlayers, whereby the whole electric charges are balanced. Smectite or expandable mica which are the expandable layer silicate has a cation exchange ability and its interlayer is easily expandable. Also, it is dispersed in water to form a sol and has a particular property that it shows a thixotropic property by forming a gel when the concentration becomes high. By utilizing this characteristic thereof, the expandable layer silicate has been used for a component of drilling mud, a sand binder for casting, and a gellant for an aqueous system.
Further, the smectite type clay can be formed into a complex by the reaction with various cationic organic or inorganic compounds. As an example of such an organic complex, an organophilic clay in which a dimethyldioctadecyl ammonium ion, which is a quaternary ammonium ion, is introduced between sheets of a smectite by cation exchange has been industrially produced and used as a gellant of a coating. However, this complex has a drawback that an organic solvent which can be gelled by dispersing it is limited to a low polar solvent such as toluene and xylene. As a gellant of a polar solvent, there has been also known an organophilic clay in which a dimethylbenzyloctadecyl ammonium ion is introduced in interlayers of a smectite by cation exchange, but it has not exhibited a sufficient gelling effect for using in industrial processes as a gellant for a high polar organic solvent.
On the other hand, there has been also known a gellant for an organic solvent, to which an affinity is imparted by modifying the surface of fine silica with an organic substance, but it has drawbacks that if it is not used in a large amount, a gelling effect cannot be obtained, and the affinity to a solvent is low, so that when used for a long time, a part thereof is deposited and it becomes difficult to carry out redispersion.
The above existing gellants for an organic solvent have drawbacks that they hardly give a sufficient gelling effect when used with a high polar organic solvent such as alcohols, ketones, ethers, halogenated hydrocarbons and amides, and they cannot stand use for a long time. Thus, development of an organophilic clay which has a high affinity to a high polar organic solvent and can be used as a gellant stably for a long time has been demanded.